Rheostat



June 5, 1956 H. MCK. STEELE RHEOSTAT Filed March 2, 1953 United States Patent RHEOSTAT Horace McKay Steele, Huntington, Ind., assignor to Model Engineering & Manufacturing, Inc, Huntington, Ind., a corporation Application March 2, 1953, Serial No. 339,667

6 Claims. (Cl. 201-48) This invention relates generally to rheostats and more particularly to rotatable brush-type rheostats.

Conventional rheostats include an insulating member for supporting a coil of resistance wire together with a rotatable brush member connected to an adjustable control shaft. Different types of resistor windings require different degrees of pressure between the contact brush and the wire. In accordance with conventional practice it is necessary to alter the basic construction of the rheostat in order to obtain the proper degree of pressure between the brush and the resistor coil. Also, conventional rheostat structures fail to provide against back lash or lost motion between the control shaft or the control knob and the movable brush. This impairs the accuracy of adjustment of the control knob with respect to the contact brush.

Accordingly, the principal object of this invention is to provide a rheostat wherein there is no back lash or lost motion between the control knob and the brush contact.

Still another object of this invention is to provide a rheostat construction adapted to receive different types of resistance coils and in conjunction therewith a brush contact control mechanism of such character that it will cooperate efficiently with the different types of resistance coils.

In accordance with this invention there is provided a rheostat comprising a ceramic base and a ceramic resistance coil support, the ceramic base being provided with a brush contact control member wherein there is positive connection of the brush with the control knob which eliminates lost motion or backlash.

In accordance with another feature of this invention, there is provided a rheostat having a base member and a resistance coil supporting member adapted to receive resistance coils of different types requiring different degrees of brush contact pressure, and a brush control mechanism including structure adapted to receive brush contact pressure springs of different characteristics, thereby to provide selected brush contact pressure in accordance with the particular type of resistance coil.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a bottom plan view of a rheostat having the construction provided in accordance with this invention.

Fig. 2 is an enlarged cross sectional view taken on line 2--2 of Fig. 1.

Fig. 3 is a detail view of the brush supporting assembly.

Fig. 4 is a partial cross section view taken on line 44 of Fig. 2.

Referring to the drawings, there is provided in accordance with this invention a rheostat having a base of ceramic or other insulating material and including a conical and centrally disposed projection 11. A ceramic core 12, having a resistance coil 13 wound about its outer surface, may be cemented or otherwise attached to the inner periphery of the base 10. In accordance with conice ventional practice the coil 13 is covered with thermoplastic insulating material, except on the top surface 14, which is adapted to be contacted by an adjustable brush contact. The ends of coil 13 are provided with collar straps 15, 15, the collar portions of which fit over the ends of core 12 in electrical connection with the ends of coil 13 and the strap portions of which provide for soldered connection to a conductor.

The bushing 16 is mounted in the central aperture 17 of base 10 and secured thereto by a nut 18 which cooperates with the head 19, thereby to clamp the bushing to the base.

Bushing 16 rotatably supports a shaft 20 on which may be mounted a control knob 21 by means of a set screw 22 engaging the flattened portion 23 of shaft 20 in accordance with conventional practice. The head 19 of bushing 16 may be hexagonal or square, and the recessed portion 24 of base 10 may similarly be hexagonal or square, whereby bushing 16 can not rotate with respect to the base 10 when the knob 21 is rotated. A washer 25 having an upturned ear 26 is mounted on bushing 16 beneath nut 18 with ear 26 nesting in one of a plurality of recesses 27 and projected outwardly thereof for engagement with a hole or slot in a mounting panel. Bar 26 thus prevents rotation of the assembly when the assembly is mounted on the rear of a central panel with bushing 16 projecting therethrough with knob 21 on the front side thereof.

A ceramic hub 29 may be mounted on the other end of shaft 20 and fixed thereto by means of a square plate 30 welded to the end of shaft 20. The walls of aperture 31 in hub 29 form a square aperture for receiving plate 30 whereby the hub can not turn on shaft 20. It is found in practice that plate 30 expands sufficiently during the welding operation to firmly engage the walls of the square aperture 31 in hub 29, thereby to prevent any back lash or lost motion between shaft 20 and hub 29.

On shaft 20 between the head 19 of bushing 16 and the lower surface of aperture 24 there is provided a stop ring 33 having an upturned U-shaped projection 34 which fits within a groove 35 in the interior wall 36 of projection 11 on base 10. Stop ring 33 is provided with hexagonal side portions which engage with the hexagonal walls of the recess 24, whereby the U-shape projection 34 and the hexagonal sides of ring 33 cooperate with projection 11 to provide an immovable stop. A stop washer 33 having an outwardly projecting car 39 may be welded on shaft 20 so that the ear 39 may engage with either side of the U-shape projection 34 to establish the limits of rotational movement of shaft 20. This structure provides a strong, positive stop mechanism for the rheostat and it is intended that stop washer 38 be positioned to stop rotation of shaft 20 with the contact brush (to be described subsequently) in contact with the respective collar straps 15.

The brush mechanism consists of a brush holder 40 having a square aperture 41 adapted to engage with the exterior square shank portion 42 of hub 29. Aperture 41 is formed by punching out a pair of oppositely disposed ears 44 and 45 which may be pre-formed at such an angle with respect to the brush holder 40 that they are bent outwardly slightly when mounted on the hub 29. This insures a tight fit between the brush holder 40 and hub 29 whereby lost motion or back lash is eliminated. Brush holder 40 also includes an ear portion 47 which is adapted to be bent over into engagement with a flattened, bevelled surface 48 on the head of hub 29. This structure prevents any tipping motion of the brush holder with respect to hub 29.

Brush holder 40 includes an outwardly extending brush-holding portion 50 having downwardly extending wall members 51, 52 and 53 which form a box-like receptacle for a carbon brush contact 55. Brush holder 40 maintains brush 55in alignment with the exposed surfaces of resistance coil 14 as the knob 21 is rotated. For holding the brush 55 in contact with resistor coil 14 under predetermined pressure, there is provided a spring 56 having a loop portion 57 in engagement with brush 5 and a'pair of leg portions 58 and d9 projecting through eye members 60 and 61 formed in the body portion of the holder 49. The eye members 60 and 61 are dimensioned to provide a relatively tight support for spring 56 whereby the spring exerts a certain predet rmined pressure on brush 55.

The brush member '55 may be connected 'by means of a conductor 63 to a washer '64 having a square aperture therein adapted to fit over the square shank 42 of hub 29 whereby it rotates with shaft 2s. The washer '64 is supported by means of a washer 6'7 fixedly mounted on th'eupper surface of the projection it of base it). Washer '67 includes a strap 68 for providing a soldered co'nnec' tion to a conductor. For insuring positive electrical contact between washers a4 and 67 there is provided a compression spring 69 which rests between the lower surface of brush holder 40 and the upper surface of washer 64. A snap ring 7% fits in a groove (not shown) in shaft 20 and engages the outer end of bushing 16 to hold the shaft therein against the force of spring 69.

From the foregoing description it Will be apparent that the brush contact is mounted to rotate with shaft '20 without any back lash or lost motion. Furthermore, a positive stop mechanism is provided which makes it possible to accurately and positively position the brush contact at the ends of the resistor coil and in positive contact with the conductor straps mounted at the ends of the resistor coil.

The invention also presents the advantage that the rotatable brush mounting assembly, which consists of all the parts mounted on shaft 16, may be stockpiled and installed in combination with any brush pressure spring which may be required for use in conjunction with any particular resistance coil. As mentioned hereinbefore, different types of resistance coils require different degrees of brush pressure, and hence it is necessary to provide brush contact pressure springs which are in a sense matched to the requirements of a particular resistance coil.

The invention claimed is:

1. In a rheostat having a base member for supporting an annular resistance coil, a brush control assembly adapted to be rotatably mounted in said base comprising a shaft, a square hub mounted on said shaft and including a head having an internal rectangular recess therein, a rectangular driving plate fixed to the end of said shaft and engaging the walls of said rectangular recess with positive pressure for providing positive engagement between said shaft and said hub, a brush holder mounted on said hub and including a rectangular aperture for receiving the square portion of said hub, said holder including an ear engaging said head and oppositely disposed ear portions bent to exert pressure on said hub to provide positive engagement between said hub and said holder.

2. Ina rheostat having a base member for supporting an annular resistance coil, a brush control assembly adapted to be rotatably mounted in said base comprising a shaft, a square hub mounted on said shaft and including a rectangular recess therein, a rectangular driving plate fixed to the end of said shaft and engaging the walls of said rectangular recess for providing positive engagement between said shaft and said hub, a brush holder mounted on said hub and including a rectangular aperture for receiving the square portion of said hub, said holder including oppositely disposed ear portions bent to exert pressure on said hub to provide positive engagement between said hub and said holder.

3. in a. rheostat having a base member for supporting an annular resistance coil, a brush control assembly adapted to be rotatably mounted in said base comprising a shaft, a plural sided hub mounted on said shaft and including a plural sided recess therein, a plural sided driving plate fixed to the end of said shaft and engaging the walls of said recess for providing positive engagement between said shaft and said hub, a brush holder mounted on said hub and including a plural sided aperture for receiving said hub, said holder including car portions bent to exert pressure on said hub to provide positive engagement between said hub and said holder.

4. A rheostat comprising an insulating base, a control shaft rotatably mounted centrally of said base, a resistance coil disposed concentrically of said shaft on said base, an insulating hub fixed to said shaft, a brush and brush holder mounted on said hub in locked relation thereto, a conductor receiving terminal mounted on said base coaxially with said shaft, a rotatable washer member locked to said shaft and including an electrical connection aligned with said brush whereby said brush and conned tion rotate as a unit, said washer being superimposed on said terminal in sliding relation thereto, and spring means compressed between said brush holder and said washer for providing pressure contact between said terminal and said washer.

5. A rheostat comprising an insulating base, a control shaft assembly rotatably mounted centrally of said base, a resistance coil disposed concentrically of said shaft on said base, said shaft assembly including an insulated brush and brush holder, a conductor receiving terminal mounted on said base coaxially with said'shaft, a rotatable washer member locked to said shaft and including an electrical connection aligned with said brush whereby said brush and connection rotate as a unit, said washer engaging 'said terminal in sliding relation thereto, and spring means for providing pressure contact between said terminal and said washer.

insulated brush for sliding contact with said coil, a stationary conductor receiving terminal mounted on said base, a washer lockedto said shaft and including an electrical connection aligned with "said brush whereby said brush and washer rotate as a unit, and means engaging said washer with said terminal.

References Citedin the file of this patent UNITED STATES PATENTS 2,040,278 Siegel May 12, 1936 2,148,785 Stoekle Feb. 28, 1939 2,576,044 Richman et al. Nov. 20, 1951 

